Why?

A lot of good points made by many others but here is a big one.

A stock 5.7 Head from 2003-3009 flows around 280 CFM, this is as much as an unported W race head. Ported 6.1 Heads flow over 350 CFM. These are huge numbers with relatively small ports that allow big HP numbers with relatively mild cam shafts. A stock 5.7 Head, a head designed to feed 345 cubic inches flows more than a fully ported 440 906 head.

A 6.1L Hemi with a cam with .550 lift, a set of headers, and a good tune puts out 500HP at the flywheel. This is out of 372 cubic inches. 25 years ago a 500 HP small block was a beast, saying you had 400 HP was a big deal. Today with a Gen III Hemi if you're not making 400-500 HP you're simply not trying. Hell a trained chimp could get 500 HP out of a Gen III Hemi.

Regards,

Joe Dokes